1. Field of the Invention
The invention is in the field of deferred action, water activated electric cells, methods of making them, and survival lamps embodying them.
2. Description of the Prior Art
Deferred action or reserve type electric cells for use as emergency or survival equipment utilizing a magnesium anode and a silver halide cathode, and adapted for activation by the addition of an aqueous fluid, have been known in the art for some time. Magnesium is a preferred anode material for such deferred action cells because it is high in the electromotive series, has good structural strength yet is light in weight, is easy to form, and is readily available. However, magnesium is very active chemically, and therefore readily corrodes from handling, from exposure to the atmosphere and particularly the damp, salty atmosphere of a marine environment where survival equipment is commonly used, and from proximity to some chemicals and in particular chemical salts employed in an electrolyte solution for the cell.
Primarily because of this problem of corrosion of the magnesium anode, prior art deferred action electric cells adapted for emergency or survival use have not included any electrolyte material therein, either in dried form or as a liquid solution, and accordingly in order to activate such cells it was necessary to add a whole or complete electrolyte solution thereto. This generally restricted such deferred action cells to usage in connection with ocean survival equipment, wherein the salt water provided the necessary whole electrolyte required for activation. Such usage of sea water as the electrolyte resulted in less than optimum activation because sea water is not a saturated salt solution. Also, such salt water activated cells were generally complicated physically by the need for controlled entrance passages, fluid flow separators, chambers to accommodate an accumulation of flake-off from the magnesium anode, and the like.
Example of prior patents disclosing such deferred action electric cells embodying magnesium anodes and silver halide cathodes which require the addition of a whole or complete electrolyte, and which are accordingly generally restricted to use in a salt water environment, are the following U.S. Pat. Nos.:
Warner et al: 2,663,749 PA1 Lockwood: 2,896,067 PA1 Armitage: 3,326,724
While both the Warner U.S. Pat. No. 2,663,749 and the Armitage U.S. Pat. No. 3,326,724 suggest that fresh water could be used as the electrolyte, and in this connection the Armitage patent suggests the electrolyte can be formed of water along with the reaction product salts from the electrolytic action, nevertheless, fresh water is an exceedingly poor electrolyte, and if it is the only electrolyte added for activating the cell, activation will be much too slow, and the resulting current capability of the cell much too low, for reliable and satisfactory operation of the cell in emergency or survival equipment.
Because the corrosiveness of the magnesium anode material has in the past tended to make deferred action electric cells generally unreliable after an extended shelf life, and therefore generally inadequate for use in emergency or survival equipment, there have been prior art attempts to provide a satisfactory corrosion-resistant coating on the magnesium. However, heretofore the procedures and chemical actions required to produce such corrosion-resistant coatings on the magnesium have been so complex, time-consuming and expensive that they have not been generally satisfactory. The Warner et al U.S. Pat. No. 2,663,749 referred to above describes one such magnesium coating procedure; and the Gruber et al U.S. Pat. No. 3,303,054 describes another complex magnesium coating procedure which is employed in the manufacture of "dry cells" which are not of the delayed action type and therefore have a limited shelf life and reliability not suitable for survival equipment.